Setting MIN MAX CONN_INTERVAL

[Minh]

Hi everybody!

I am working with ANCS (nrf51822 SDK 9.0) I am confusing on setting the connection parameters which are MIN an MAX connection interval.

Firstly, I set MIN_CONN_INTERVAL = MAX_CONN_INTERVAL = 1000ms the ANCS notifications come right after I got phone notification (message, phone call). But when I set MIN_CONN_INTERVAL = 500ms and MAX_CONN_INTERVAL = 800ms, the ANCS notification come slower than previous setting. It does not make me sense.

Could you please give me explanation for this? Is it possible to set MIN_CONN_INTERVAL = MAX_CONN_INTERVAL ?

Thank you very much.

[Anders Strand]

Hi. The connection interval is in reality decided by the central device (the phone). The peripheral device can request a certain interval, but the central does not have to accept it. Do you have an extra nRF51 you can set up as an nRF sniffer and capture the connection event?

[James Yu]

Take a look at Apple's Bluetooth Design Guidelines: developer.apple.com/.../BluetoothDesignGuidelines.pdf

3.6 Connection Parameters
The accessory isresponsible for the connection parameters used for the Low Energy connection. The accessory
should request connection parameters appropriate for its use case by sending an L2CAP Connection Parameter
Update Request at the appropriate time. See the Bluetooth 4.0 specification, Volume 3, Part A, Section 4.20 for
details. The connection parameter request may be rejected if it does not comply with all of these rules:
● Interval Max * (Slave Latency + 1) ≤ 2 seconds
● Interval Min ≥ 20 ms
● Interval Min + 20 ms ≤ Interval Max Slave Latency ≤ 4
● connSupervisionTimeout ≤ 6 seconds
● Interval Max * (Slave Latency + 1) * 3 < connSupervisionTimeout

So if MIN_CONN_INTERVAL = MAX_CONN_INTERVAL, it could be rejected since it doesn't satisfy #3

[Minh]

What is Interval Max Slave Latency ? is it same as Interval Max ? if yes, why do they call it Interval Max Slave Latency ?

[James Yu]

I think that's an typo, it should just be Interval Max, and slave latency should be a separate point.

[Minh]

Ah, I see. So do you what is real connection interval value if 3-rd condition is not satisfied ?